The use of specific admixtures during the milling process of cements has been known since the 1930's. Milling admixtures--milling intensifiers--are substances that prevent the aggregation of particles or help scatter the grist during the milling process. The milling admixtures must not adversely affect the qualities of cements. The milling admixtures further inhibit the grist from sticking to the milling bodies, thereby increasing the output of the mill. The use of milling admixtures reduces the cost of milling and enables the production of high quality cements. The milling admixtures also ameliorate the starting resistance and the processes of emptying silos and/or the storage life of cements.
Actually, several substances are used as milling admixtures for the production of cements, especially Portland cements, such as calcium ligninsulphonate containing no monosaccharides, a mixture of triethanolamine with calcium ligninsulphonate, different types of fatty acids, different types of diolefins, especially glycols, and many other commercial mixtures. (W. H. Duda, Cement Data Book, 1985). In the Federal Republic of Germany liquid milling admixtures, such as aminoacetate, ethylene glycol or propylene glycol, are used for the production of PC 550 (O. Labahn and B. Kohlhaas, Ratgeber fur Zement-Ingenieure, 1982). Most of the research done in this field is oriented towards gaining new milling admixtures having the following properties: positive influence on the milling process, reduction of power consumption in milling, greater specific surface of the product, and no negative influence on the qualities of cements. Many substances that positively influence the milling process of cements have been mentioned in technical literature and patents. Lists and surveys of these substances are to be found in Cement Research Progress, 1974-1978, for example.
Related to the problem of milling admixtures is the set of problems concerning the new type of inorganic hydraulic binding agents, i.e., gypsumless cements. These cements are based on the Portland clinker or white cement and are ground in the absence of gypsum. The regulating influence of the gypsum is supplemented by the synergistically acting mixture of alkaline metals, e.g., carbonates, hydrogen carbonates, silicates and hydroxides, and sulphonated polyelectrolytes, such as derivatives of lignin, sulphonated polyphenolates or other liquefying agents used as plasticizers. Gypsumless Portland cements are outstanding because of their superior qualities compared to common Portland cements, especially in the preparation of pastes, mortars, and concretes having a substantially lower cement-water ratio. The properties of these gypsumless cements have been already described, e.g., in the Czech author's certificate 257 315. These properties of gypsumless cements also can be attained by increasing the milling fineness beyond that of common Portland cements.
The above solutions have been directed, however, to attaining a higer specific surface for cements only. Another solution for problems of gypsumless cements has been presented in U.S. Pat. No. 3,689,294 (Brunauer). In the '297 patent, as in M. Yudenfreund's publication and in other publications, there are described hardened Portland cement pastes of low porosity (Cement and Concrete Research 2:313-330, 1972), compositions of liquid pastes or mortars and concretes in the expanding state, based on ground cement clinkers of specific surfaces from 600 to 900 m.sup.2 /kg, containing at least 0.002 parts of milling admixtures and at least 0.0025 parts of alkaline earth ligninsulphonates or sulphonated lignin and at least 0.0025 parts of alkaline carbonates with a cement-water ratio in the range of from 0.20 to 0.28. These publications specify the following milling admixtures: Kraft lignin (alkali lignin), oleic acid, diethylcarbonate, ethoxylated nonylphenols with different numbers of ethoxyl groups, sodium dodecylbenzylsulphonate, mixtures of alkylsulphonates and sulphocarboxylates, sulphosuccinates, alkylated sulphosuccinates, and/or sulphosuccinates with amines and alkylsulphates or with alkylphenylpolyglycol ethers, triethanolamine, ethylene glycol, and alkylphenylsulphonates. The main feature of milling admixtures is the simultaneous presence of polar and non-polar groups in a molecule. It was not possible to prepare gypsumless cement compositions of low cement-water ratio with the given workability using Brunauer's criterion (U.S. Pat. No. 3,689,294) since the matter is unstable in alkaline medium. Stable adsorption of matter onto the surface of the cement in alkaline medium is necessary since admixtures that replace gypsum, e.g., soda and ligninsulphonate, form solutions with pH up to 11.5. Furthermore, the combination of clinker and water produces a very alkaline and limy medium. Other matters, though stable in the alkaline medium, have no wetting property for powder materials, e.g., triethanolamine, silanes, siloxanes, and stearates, so that they can not be used for the preparation of gypsumless cement compositions with a low cement-water ratio.
From all matters known up to now and applied as admixtures for the milling of Portland clinkers for gypsumless cements, only one single matter produces the requisite effects and it is, according to the invention, the triethanolamide of dodecylbenzylsulphonic acid. Its application, however, was accidental until now, when, according to the present invention, it was shown to be important for conditions in the milling of Portland clinkers.